1. Field of the Invention
The present invention relates to a magnetic recording apparatus having an inductive head as a means for recording information on magnetic recording medium (a flexible disk or the like).
2. Description of the Prior Art
FIG. 6 is a block diagram showing an example of the configuration of a conventional magnetic recording apparatus. In the magnetic recording apparatus shown in this figure, when information is going to be recorded on a magnetic recording medium, write data DWR is fed from a host (not shown) to a write driver 100. The write driver 100, on the basis of the write data DWR fed thereto, switches the direction of a write current IWR that is fed to an inductive head 110 (hereinafter referred to as the “head 110”). As a result of this operation, the magnetic recording medium is magnetized in the direction that conforms to the write current IWR flowing through the head 110, and in this way the writing of the write data DWR is achieved.
Here, the write current IWR is proportional to a control current IWRref fed from a write current setting circuit 101 to the write driver 100. The write current setting circuit 101 is a circuit that varies the control current IWRref (and thus the write current IWR) according to a control signal CNT fed from the host.
Moreover, the conventional magnetic recording apparatus is provided with many detection circuits, such as a first write unsafe detection circuit 105 (hereinafter referred to as the “first WUS circuit 105”) having comparators 102 and 103 in the input stage thereof and a second write unsafe detection circuit 109 (hereinafter referred to as the “second WUS circuit 109”) having comparators 106 and 107 in the input stage thereof. These many detection circuits are circuits that detect various faults in the head 110 on the basis of the results of comparison between head voltages HX and HY appearing at both ends of the head 110 and predetermined reference voltages (for the first and second WUS circuits 105 and 109, a first and a second reference voltage Vref1 and Vref2 respectively).
As shown in the figure, to the non-inverting input terminals (+) of the comparators 102 and 103 is connected a first direct-current voltage source 104 (the first reference voltage Vref1), and to the non-inverting input terminals (+) of the comparators 106 and 107 is connected a second direct-current voltage source 108 (the second reference voltage Vref2). Moreover, to the inverting input terminals (−) of the comparators 102 and 106 is connected one end of the head 110 (the head voltage HX), and to the inverting input terminals (−) of the comparators 103 and 107 is connected the other end of the head 110 (the head voltage HY). The output terminals of the comparators 102 and 103 are connected individually to the input terminals of the first WUS circuit 105, and the output terminals of the comparators 106 and 107 are connected individually to the input terminals of the second WUS circuit 109.
The first WUS circuit 105, on the basis of the results of comparison between the head voltages HX and HY and the first reference voltage Vref1, detects faults of an abnormally low frequency in the write data DWR, short-circuiting of the head 110 to the supply voltage Vcc, and short-circuiting of the head 110 to the ground voltage GND. These faults are detected by recognizing the trailing edges of back electromotive forces that appear in the head voltages HX and HY in response to the write data DWR. Therefore, it is necessary to set the threshold level of the comparators 102 and 103 (i.e. the first reference voltage Vref1) at the optimum value that permits as correct detection as possible of the various defects mentioned above. Alternatively, it is necessary to provide a plurality of circuits similar to those described above so that the optimum reference voltages for the detection of various faults can be set individually.
On the other hand, the second WUS circuit 109 latches the results of comparison between the head voltages HX and HY and the second reference voltage Vref2 in synchronism with the write data DWR, and detects a fault of the head 110 being brought into an open state on a logical basis according to the latched output. Here, the comparison operation by the comparators 106 and 107 involves simply detecting abnormal waveforms in the head voltages HX and HY, and therefore the setting of the threshold level of these comparators 106 and 107 (i.e. the second reference voltage Vref2) is not so critical as the setting of the first reference voltage Vref1 mentioned above. Therefore, the second reference voltage Vref2 is set at as high a voltage as possible (close to the supply voltage Vcc) so that trailing edges in the head voltages HX and HY can be detected without delay.
The first and second WUS circuits 105 and 109 feed the results of their respective fault detection described above in the form of fault detection signals WUS1 and WS2 to the host. When the host recognizes a fault in the head 110 on the basis of these abnormal detection signals WUS1 and WUS2, it performs an operation that ensures the writing to the magnetic recording medium (for example, a write-disable or reset operation).
FIG. 7 is a diagram showing the relationship among the head voltages Va to Vd, the first and second reference voltages Vref1 and Vref2, and the write current IWR in the conventional magnetic recording apparatus. In this figure, Va represents the peak voltage of trailing edges that appear in the head voltages HX and HY due to back electromotive forces, and Vb represents the short-circuit voltage that appears when one end of the head 110 is short-circuited to the supply voltage Vcc. Moreover, Vc represents the short-circuit voltage that appears when one end of the head 110 is short-circuited to ground, and Vd represents the open voltage that appears when the head 110 is brought into an open state.
As shown in the figure, the behavior of the head voltages HX and HY (as represented by the specific voltages Va to Vd they take) varies greatly depending on the write current IWR. By contrast, the first and second reference voltages Vref1 and Vref2, which are provided to permit the detection of faults in the head 110, are, as described above, kept constant, irrespective of the write current IWR. As a result, there exists a range within which the write current IWR is restricted to ensure correct detection of faults in the head 110. That is, quite inconveniently, if the write current IWR is varied out of the range, faults cannot be detected correctly.
Specifically, with the write current IWR larger than a predetermined value, the short-circuit voltage Vb associated with the supply voltage Vcc is lower than the first reference voltage Vref1. Thus, even if one end of the head 110 is short-circuited to the supply voltage Vcc, the head 110 is recognized as functioning normally. Conversely, with the write current IWR smaller than a predetermined value, the peak voltage Va associated with back electromotive forces is higher than the first reference voltage Vref1. Thus, even if the head 110 is functioning normally, it is recognized as being short-circuited to the supply voltage Vcc.
The behavior of the head voltages HX and HY varies also depending on the supply voltage Vcc, and therefore, just as with the write current IWR mentioned above, there exists also a range within which the supply voltage Vcc is restricted to permit correct detection of faults in the head 110.
Moreover, the conventional magnetic recording apparatus is so configured as to detect various faults in the head 110 on the basis of the results of comparison between the head voltages HX and HY appearing at both ends of the head 110 and at least two reference voltages (the first and second reference voltages Vref1 and Vref2), and is thus provided with at least two write unsafe detection circuit (the first and second WUS circuits 105 and 109) as a means for detecting faults. Thus, quite inconveniently, the conventional magnetic recording apparatus inevitably requires a large chip area and a large number of circuit elements at accordingly high cost.